1. Field of the Invention
The present invention relates to linear synchronous motors, and more specifically, it relates to the detection of phasing of a linear synchronous motor.
2. Description of Related Art
Linear synchronous motor (LSM) drive systems, such as those employed on magnetic levitation trains utilizing Halbach arrays, are well known in the art and employ multi-phase AC or pulsed windings in the track interacting with permanent-magnet assemblies on the moving vehicle to produce propulsion or dynamic braking. In order for the LSM drive to function, it is necessary that the location of the Halbach array with respect to the windings be known at all times within a small fraction of the wavelength of the Halbach arrays. This information is then fed to the drive circuitry to control its output as a function of time. In the past, various techniques to accomplish this end have been used. These include the use of optical position sensing systems employing lasers and photocells on the moving vehicle and a strip with alternating black and white bands embedded in the track. Alternatively, to determine the position, special windings are embedded in the track that receive a radio signal from a compact radiator on the moving vehicle. Neither of these system types is totally satisfactory. The optical system suffers from the effects of dirt (or, in the winter, snow) on its banded strip, and the radio system is subject to interference from the high-current drive pulses in the LSM track windings.